java.awt
class List

java.lang.Object java.awt.Component java.awt.List

All Implemented Interfaces:

ItemSelectable, MenuContainer, ImageObserver, Serializable, Accessible

Most common way to construct:

List lst = new List(4, false);

Based on 28 examples

public class List
extends Component
implements ItemSelectable, Accessible

The List component presents the user with a scrolling list of text items. The list can be set up so that the user can choose either one item or multiple items.

For example, the code . . .

 List lst = new List(4, false);
 lst.add("Mercury");
 lst.add("Venus");
 lst.add("Earth");
 lst.add("JavaSoft");
 lst.add("Mars");
 lst.add("Jupiter");
 lst.add("Saturn");
 lst.add("Uranus");
 lst.add("Neptune");
 lst.add("Pluto");
 cnt.add(lst);
 

where cnt is a container, produces the following scrolling list:

If the List allows multiple selections, then clicking on an item that is already selected deselects it. In the preceding example, only one item from the scrolling list can be selected at a time, since the second argument when creating the new scrolling list is false. If the List does not allow multiple selections, selecting an item causes any other selected item to be deselected.

Note that the list in the example shown was created with four visible rows. Once the list has been created, the number of visible rows cannot be changed. A default List is created with four rows, so that lst = new List() is equivalent to list = new List(4, false).

Beginning with Java 1.1, the Abstract Window Toolkit sends the List object all mouse, keyboard, and focus events that occur over it. (The old AWT event model is being maintained only for backwards compatibility, and its use is discouraged.)

When an item is selected or deselected by the user, AWT sends an instance of ItemEvent to the list. When the user double-clicks on an item in a scrolling list, AWT sends an instance of ActionEvent to the list following the item event. AWT also generates an action event when the user presses the return key while an item in the list is selected.

If an application wants to perform some action based on an item in this list being selected or activated by the user, it should implement ItemListener or ActionListener as appropriate and register the new listener to receive events from this list.

For multiple-selection scrolling lists, it is considered a better user interface to use an external gesture (such as clicking on a button) to trigger the action.

List

public List()
     throws HeadlessException

Creates a new scrolling list. By default, there are four visible lines and multiple selections are not allowed. Note that this is a convenience method for List(0, false). Also note that the number of visible lines in the list cannot be changed after it has been created.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

List

public List(int rows)
     throws HeadlessException

Creates a new scrolling list initialized with the specified number of visible lines. By default, multiple selections are not allowed. Note that this is a convenience method for List(rows, false). Also note that the number of visible rows in the list cannot be changed after it has been created.

Parameters:

rows - the number of items to show.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

List

public List(int rows,
            boolean multipleMode)
     throws HeadlessException

Creates a new scrolling list initialized to display the specified number of rows. Note that if zero rows are specified, then the list will be created with a default of four rows. Also note that the number of visible rows in the list cannot be changed after it has been created. If the value of multipleMode is true, then the user can select multiple items from the list. If it is false, only one item at a time can be selected.

Parameters:

rows - the number of items to show.

multipleMode - if true, then multiple selections are allowed; otherwise, only one item can be selected at a time.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

add

public void add(String item)

Adds the specified item to the end of scrolling list.

Parameters:

item - the item to be added

add

public void add(String item,
                int index)

Adds the specified item to the the scrolling list at the position indicated by the index. The index is zero-based. If the value of the index is less than zero, or if the value of the index is greater than or equal to the number of items in the list, then the item is added to the end of the list.

Parameters:

item - the item to be added; if this parameter is null then the item is treated as an empty string, ""

index - the position at which to add the item

addActionListener

public synchronized void addActionListener(ActionListener l)

Adds the specified action listener to receive action events from this list. Action events occur when a user double-clicks on a list item or types Enter when the list has the keyboard focus.

If listener l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

Parameters:

l - the action listener

addItem

public void addItem(String item)

Parameters:

item

addItem

public synchronized void addItem(String item,
                                 int index)

Parameters:

item

index

addItemListener

public synchronized void addItemListener(ItemListener l)

Adds the specified item listener to receive item events from this list. Item events are sent in response to user input, but not in response to calls to select or deselect. If listener l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

Parameters:

l - the item listener

addNotify

public void addNotify()

Creates the peer for the list. The peer allows us to modify the list's appearance without changing its functionality.

Overrides:

addNotify in class Component

allowsMultipleSelections

public boolean allowsMultipleSelections()

clear

public synchronized void clear()

countItems

public int countItems()

delItem

public void delItem(int position)

Parameters:

position

delItems

public synchronized void delItems(int start,
                                  int end)

Parameters:

start

end

deselect

public synchronized void deselect(int index)

Deselects the item at the specified index.

Note that passing out of range parameters is invalid, and will result in unspecified behavior.

If the item at the specified index is not selected, then the operation is ignored.

Parameters:

index - the position of the item to deselect

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this List. For lists, the AccessibleContext takes the form of an AccessibleAWTList. A new AccessibleAWTList instance is created, if necessary.

Overrides:

getAccessibleContext in class Component

Returns:

an AccessibleAWTList that serves as the AccessibleContext of this List

getActionListeners

public synchronized ActionListener[] getActionListeners()

Returns an array of all the action listeners registered on this list.

Returns:

all of this list's ActionListeners or an empty array if no action listeners are currently registered

getItem

public String getItem(int index)

Gets the item associated with the specified index.

Parameters:

index - the position of the item

Returns:

an item that is associated with the specified index

getItemCount

public int getItemCount()

Gets the number of items in the list.

Returns:

the number of items in the list

getItemListeners

public synchronized ItemListener[] getItemListeners()

Returns an array of all the item listeners registered on this list.

Returns:

all of this list's ItemListeners or an empty array if no item listeners are currently registered

getItems

public synchronized String[] getItems()

Gets the items in the list.

Returns:

a string array containing items of the list

getListeners

public EventListener[] getListeners(Class listenerType)

Returns an array of all the objects currently registered as FooListeners upon this List. FooListeners are registered using the addFooListener method.

You can specify the listenerType argument with a class literal, such as FooListener.class. For example, you can query a List l for its item listeners with the following code:

ItemListener[] ils = (ItemListener[])(l.getListeners(ItemListener.class));

If no such listeners exist, this method returns an empty array.

Overrides:

getListeners in class Component

Parameters:

listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener

Returns:

an array of all objects registered as FooListeners on this list, or an empty array if no such listeners have been added

getMinimumSize

public Dimension getMinimumSize()

Determines the minimum size of this scrolling list.

Overrides:

getMinimumSize in class Component

Returns:

the minimum dimensions needed to display this scrolling list

getMinimumSize

public Dimension getMinimumSize(int rows)

Gets the minumum dimensions for a list with the specified number of rows.

Parameters:

rows - number of rows in the list

Returns:

the minimum dimensions for displaying this scrolling list given that the specified number of rows must be visible

getPreferredSize

public Dimension getPreferredSize()

Gets the preferred size of this scrolling list.

Overrides:

getPreferredSize in class Component

Returns:

the preferred dimensions for displaying this scrolling list

getPreferredSize

public Dimension getPreferredSize(int rows)

Gets the preferred dimensions for a list with the specified number of rows.

Parameters:

rows - number of rows in the list

Returns:

the preferred dimensions for displaying this scrolling list given that the specified number of rows must be visible

getRows

public int getRows()

Gets the number of visible lines in this list. Note that once the List has been created, this number will never change.

Returns:

the number of visible lines in this scrolling list

getSelectedIndex

public synchronized int getSelectedIndex()

Gets the index of the selected item on the list,

Returns:

the index of the selected item; if no item is selected, or if multiple items are selected, -1 is returned.

getSelectedIndexes

public synchronized int[] getSelectedIndexes()

Gets the selected indexes on the list.

Returns:

an array of the selected indexes on this scrolling list; if no item is selected, a zero-length array is returned.

getSelectedItem

public synchronized String getSelectedItem()

Gets the selected item on this scrolling list.

Returns:

the selected item on the list; if no item is selected, or if multiple items are selected, null is returned.

getSelectedItems

public synchronized String[] getSelectedItems()

Gets the selected items on this scrolling list.

Returns:

an array of the selected items on this scrolling list; if no item is selected, a zero-length array is returned.

getSelectedObjects

public Object[] getSelectedObjects()

Gets the selected items on this scrolling list in an array of Objects.

Returns:

an array of Objects representing the selected items on this scrolling list; if no item is selected, a zero-length array is returned.

getVisibleIndex

public int getVisibleIndex()

Gets the index of the item that was last made visible by the method makeVisible.

Returns:

the index of the item that was last made visible

isIndexSelected

public boolean isIndexSelected(int index)

Determines if the specified item in this scrolling list is selected.

Parameters:

index - the item to be checked

Returns:

true if the specified item has been selected; false otherwise

isMultipleMode

public boolean isMultipleMode()

Determines whether this list allows multiple selections.

Returns:

true if this list allows multiple selections; otherwise, false

isSelected

public boolean isSelected(int index)

Parameters:

index

makeVisible

public synchronized void makeVisible(int index)

Makes the item at the specified index visible.

Parameters:

index - the position of the item

minimumSize

public Dimension minimumSize()

Overrides:

minimumSize in class Component

minimumSize

public Dimension minimumSize(int rows)

Parameters:

rows

paramString

protected String paramString()

Returns the parameter string representing the state of this scrolling list. This string is useful for debugging.

Overrides:

paramString in class Component

Returns:

the parameter string of this scrolling list

preferredSize

public Dimension preferredSize()

Overrides:

preferredSize in class Component

preferredSize

public Dimension preferredSize(int rows)

Parameters:

rows

processActionEvent

protected void processActionEvent(ActionEvent e)

Processes action events occurring on this component by dispatching them to any registered ActionListener objects.

This method is not called unless action events are enabled for this component. Action events are enabled when one of the following occurs:

• An ActionListener object is registered via addActionListener.
• Action events are enabled via enableEvents.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Parameters:

e - the action event

processEvent

protected void processEvent(AWTEvent e)

Processes events on this scrolling list. If an event is an instance of ItemEvent, it invokes the processItemEvent method. Else, if the event is an instance of ActionEvent, it invokes processActionEvent. If the event is not an item event or an action event, it invokes processEvent on the superclass.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Overrides:

processEvent in class Component

Parameters:

e - the event

processItemEvent

protected void processItemEvent(ItemEvent e)

Processes item events occurring on this list by dispatching them to any registered ItemListener objects.

This method is not called unless item events are enabled for this component. Item events are enabled when one of the following occurs:

• An ItemListener object is registered via addItemListener.
• Item events are enabled via enableEvents.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Parameters:

e - the item event

remove

public void remove(int position)

Removes the item at the specified position from this scrolling list. If the item with the specified position is selected, and is the only selected item in the list, the list is set to have no selection.

Parameters:

position - the index of the item to delete

remove

public synchronized void remove(String item)

Removes the first occurrence of an item from the list. If the specified item is selected, and is the only selected item in the list, the list is set to have no selection.

Parameters:

item - the item to remove from the list

removeActionListener

public synchronized void removeActionListener(ActionListener l)

Removes the specified action listener so that it no longer receives action events from this list. Action events occur when a user double-clicks on a list item. If listener l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

Parameters:

l - the action listener

removeAll

public void removeAll()

Removes all items from this list.

removeItemListener

public synchronized void removeItemListener(ItemListener l)

Removes the specified item listener so that it no longer receives item events from this list. If listener l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

Parameters:

l - the item listener

removeNotify

public void removeNotify()

Removes the peer for this list. The peer allows us to modify the list's appearance without changing its functionality.

Overrides:

removeNotify in class Component

replaceItem

public synchronized void replaceItem(String newValue,
                                     int index)

Replaces the item at the specified index in the scrolling list with the new string.

Parameters:

newValue - a new string to replace an existing item

index - the position of the item to replace

select

public void select(int index)

Selects the item at the specified index in the scrolling list.

Note that passing out of range parameters is invalid, and will result in unspecified behavior.

Note that this method should be primarily used to initially select an item in this component. Programmatically calling this method will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

Parameters:

index - the position of the item to select

setMultipleMode

public void setMultipleMode(boolean b)

Sets the flag that determines whether this list allows multiple selections. When the selection mode is changed from multiple-selection to single-selection, the selected items change as follows: If a selected item has the location cursor, only that item will remain selected. If no selected item has the location cursor, all items will be deselected.

Parameters:

b - if true then multiple selections are allowed; otherwise, only one item from the list can be selected at once

setMultipleSelections

public synchronized void setMultipleSelections(boolean b)

Parameters:

b